4.7 Enabling Multipath I/O Support

Multipathing is the technique of creating more than one physical
path between the server CPU and its storage devices. It results in
better fault tolerance and performance enhancement. Oracle VM
supports multipath I/O out of the box. Oracle VM Servers are installed
with multipathing enabled because it is a requirement for SAN
disks to be discovered by Oracle VM Manager.

Note

Any system disks (disks that contain / or /boot) are blacklisted
by Oracle VM Manager and are not available for use in an Oracle VM
environment.

Multipath configuration information is stored in
/etc/multipath.conf and contains specific
settings for Oracle VM along with an extensive set of
configuration details for commonly used SAN hardware. In most
cases the user should not need to modify this file and is advised
not to. Examining the contents of the file may be useful to better
understand how it works in Oracle VM and what may need to be
configured if your SAN is not using multipathing and your LUNs are
not appearing.

In case user action is required to enable multipathing, this
sections explains how to do so. The required steps depend on the
storage hardware implemented. Consequently, the steps below are
intended as a guideline and priority should be given to the SAN
hardware documentation.

Note

Not all steps apply to your environment. Consult the SAN
hardware vendor's documentation for a complete list of steps,
the order in which to execute them, and their relevance to your
specific environment.

General steps to configure multipathing:

Design and document the multipathing configuration you intend
to apply to the SAN hardware used in your Oracle VM
environment.

Ensure that the drivers for your Host Bus Adapters (HBAs) are
present. If not, install the drivers.

Configure the appropriate zoning on the fibre channel
switches.

Configure LUN masking on the storage arrays.

Configure path optimization features (ALUA or similar) on your
disk subsystem, if so instructed by your vendor's
documentation.

Check the fabric information on each Oracle VM Server that has access
to the SAN hardware. Use multipath -ll and
related commands.

Make the necessary changes to the file
/etc/multipath.conf on the Oracle VM Servers.

Note

You must make the exact same changes to the multipath
configuration file on all Oracle VM Servers in your environment.

Important

It is critical that the configuration parameter
user_friendly_names remain set to
no within the
/etc/multipath.conf configuration file.

Restart the multipath daemon (multipathd).

Check the fabric information again to verify the
configuration.

If so instructed by the vendor's documentation, rebuild
initrd.

Reboot the Oracle VM Servers to verify that the SAN and multipathing
configuration come up properly after a restart.

For detailed information and instructions, consult the SAN
hardware vendor's documentation.